1. Field of the Invention
The invention relates to a rotor for an electric machine, and more particularly a transverse flow machine.
2. Description of the Related Art
Electric machines operating by the transverse flow principle are previously known from the following patent documents and patent disclosures:
1. DE 35 36 538 A1 PA1 2. DE 37 05 089 C1 PA1 3. DE 39 04 516 C1. PA1 4. DE 91 16 192 U1 PA1 5. DE 92 00 116 U1 PA1 6. EP 0 642 204 A1 PA1 7. DE 44 00 614 C2.
The basic principle and basic structure of machines operating according to the transverse flow principle are described in detail in these publications. Such electric machines can be operated both as a motor and as that of a generator.
In the described embodiments, the rotor comprises one or several axially stacked concentric rings (active rings) separated from one another by interposed rings of plastic or other electrically nonconducting material and/or a rotor disk, along the periphery of which rings so-called collectors or soft-iron elements, which typically may be constructed of axially stacked laminations, and magnets arranged alternately. These concentric rings are called pole structures.
The stability of the rotor structure, as is generally known, is obtained by gluing, and this joint is additionally secured using plain structural elements, such as bolts, screws, rivets etc. Such designs are known, e.g., from the following documents:
The magnets and collector or soft-iron elements, on the rotor taught in the document DE 91 16 192 U1, are joined together in a support structure of electrically and magnetically nonconducting material. The soft-iron elements are cast or glued together with the permanent magnets; the individual rings (support disk and pole structure) are joined together by gluing. To obtain stability, the pole structures are in a design, according to this document, equipped on both sides of the central support disk with prefabricated receiving rings that feature radially extending pocket type recesses, in which the permanent magnets are centered by themselves and are radially secured and embedded by means of a casting compound or glued. The magnets feature for that purpose, on the two radially opposed boundary faces, different axial dimensions created by an intervening shoulder, the axial dimension of the magnet in the installed position being on the outer boundary face in a radial direction smaller than the boundary face disposed inside, in radial direction. The permanent magnets are in this way precisely fitted sideways and radially, which is meant to permit them to run true with a very fine gap. Providing these receiving rings, however increases the number of components and thus the manufacturing and assembly costs. The receiving ring and adjacent components in the axial direction--for example support disk, spacer and end ring--are axially joined by gluing. The receiving rings themselves feature on their end face away from the insertion side of the magnets, a shoulder and respectively a step, that brings about a fixing of the receiving rings in radial direction, in conjunction with fasteners of complementary design, that is, in the working direction of the centrifugal forces. With varying constraints, however, the properties of the adhesives and casting compounds are very different. Generally, the strength of the adhesive diminishes with temperature and humidity fluctuations, as well as sustained loading, and simultaneously the stability of the stator. Therefore, the number of separating spots is possibly very high.
The rotor design known from the German utility model DE 92 00 116 U1 comprises collector or soft-iron elements which in the axial direction are provided with U-shaped recesses to receive the magnets. The permanent magnets and collector elements are in a peripheral direction joined by an electrically nonconducting insulation layer, for example glue. While such design includes positional fixing of the permanent magnets in a peripheral direction, such as a fixing in the radial direction, however, is given only by the electrically nonconducting insulation layer. In this design, too, the disadvantages associated with the style relative to the German utility model DE 91 16 192 U1 apply as well.
To realize small rotors where a narrow pole pitch is desired, EP 0 642 204 A1 discloses a design in which the rotor features, in the axial direction, a rotor disk attached to the rotor shaft and fastened in a concentric annular arrangement to it, the polarized magnets and magnetizable collector or soft-iron elements. The joint therebetween being established by means of fasteners that traverse the polarized magnets and attach to the rotor disk, respectively to an insulating ring which, in axial direction, is joined to the rotor disk.
A shortcoming of using these fasteners, while counteracting separating stress, is constituted primarily by the appreciable increase in rotor mass and rotor volume, and thus loss-prone active volume. The bores for threaded insert and bolt through holes provided for assembly of the fasteners require a high manufacturing and machining expense. With fasteners traversing the active rings, either the magnets must be split, i.e., provided in twice the number or, with such components traversing in the region of the collector or soft-iron elements, the latter are subject to high machining and assembly expense. In the case of a rotor designed as described in EP 0 642 204 A1, the centrifugal forces occurring at high speeds of rotation cannot be managed economically by frictional and composition-of-matter joining--notably screwing and gluing.
Known from the embodiment disclosed in DE 44 90 614 C2 is a rotor which, in addition to the support disk, comprises at least one pole structure that consists of two adjacent rows, separated by an intermediate layer of magnetically or electrically nonconducting material, of in peripheral direction, alternately magnetizable magnets with interposed collector or soft-iron elements. The magnets arranged in a pole structure in the rings of collector or soft-iron elements and magnets feature, in the installed position, at least one centering aid each on their axial boundary surfaces. Coordinated with these centering aids, on the end faces of end ring, ia a spacer ring and/or support disk facing the magnets, within mating receiving recesses. Additionally, to reduce the separation sensitivity of the adhesive, deformation zones are provided on the adjacent elements consisting of materials resistant to separation. Providing these centering elements offers the advantage of a radial form-fit between the magnets and adjacent components under the effect of centrifugal force. The position of the magnets is accurately fixed on account of the recesses, and thus at the same time the position of the collector or soft-iron elements disposed between the magnets. Providing deformation zones offers the advantage that a separation between magnets and adjacent elements is normally avoided. While such design is distinguished by a lower component expense as compared to the embodiments disclosed in the aforementioned documents, the manufacturing and assembly expense is considerably higher.
Therefore, the objective underlying the invention is to improve a rotor of the initially named type to the effect that the above disadvantages are avoided and the mechanical stability is increased without impairment of the electromagnetic properties. Along with it, the design is meant to be low-cost as it is distinguished by low manufacturing and assembly expense.